1. Field of the Invention
The present invention relates to an optical device for converting incident light into, for example, a second harmonic and outputs the second harmonic, and also relates to a manufacturing method thereof.
2. Description of the Related Art
Conventionally, the use of short-wavelength semiconductor laser beams in the field of optical recording and playback has been studied to provide high-density recording. Among such studies, optical devices generating a second harmonic are being investigated.
An optical device is disclosed in Japanese Examined Patent Application Publication No. 8-12367 and includes a piezoelectric layer having two types of regions having opposite polarization directions and the regions are arranged alternately in the direction of propagation of incident light.
In a method of manufacturing the above-described optical device, heat is selectively applied to a portion of the piezoelectric layer, which includes LiNbO3, to form the regions having opposite polarization directions.
However, in the conventional optical device, partial heat treatment is expensive and requires a lot of time and the defect rate increases due to difficulty in selectively applying heat with precision.
In order to overcome the above-described problems, preferred embodiments of the present invention provide an optical device including a substrate, dielectric layers provided on portions of the substrate, a piezoelectric layer provided on the substrate and the dielectric layers, the piezoelectric layer having first regions disposed on the substrate and second regions disposed on the dielectric layers, the first and second regions being adjacent to each other, wherein the piezoelectric layer transmits incident light substantially parallel to the surface of the piezoelectric layer, the first regions have an axis orientation in a first direction caused by the substrate, the second regions have an axis orientation in a second direction caused by the dielectric layers, the first direction is opposite to the second direction.
In the optical device according to this preferred embodiment of the present invention, the substrate preferably includes at least one material selected from the group consisting of c-plane sapphire, a-plane sapphire, m-plane sapphire, negative Z-plane LiNbO3, and negative z-plane LiTaO3, and the dielectric layers includes at least one material selected from the group consisting of SiO2, SiO, SiN, Tin, BaSiTiO3, Al2O3, TaN, TiO2, and Ta2O3.
Alternatively, in the optical device according to preferred embodiments of the present invention, the substrate includes at least one material selected from the group consisting of LiNbO3 other than negative Z-plane LiNbO3, LiTaO3 other than negative Z-plane LiTaO3, glass, and quartz crystal, and the dielectric layers include at least one of SiO2 and AlN.
In the optical device, the dielectric layers are preferably made of one of ZnO, LiNbO3, LiTaO3, KNbO3, Ta2O3, and AlN, and the material of the dielectric layers is preferably different from that of the substrate.
According to the above-described novel configuration, the piezoelectric layer generating a second harmonic is prepared with high reproducibility and at a reduced cost by forming the dielectric layers, wherein the piezoelectric layer has the first and second regions which have opposite orientations and are adjacent to each other.
In the optical device, each of the dielectric layers preferably has a refractive index that is less than that of the piezoelectric layer. In the optical device, the substrate preferably has a refractive index that is less than that of the piezoelectric layer.
According to the above-described configuration, since the piezoelectric layer has a refractive index that is less than that of at least one of the dielectric layers and the substrate, the leakage of light transmitted in the piezoelectric layer is suppressed. Thus, the loss of light is greatly reduced and the efficiency of converting incident light into a second harmonic is greatly increased.
In the optical device, the first and second directions are preferably different. The first and second directions are preferably substantially perpendicular to the direction of propagation of incident light. The first and second regions are preferably arranged alternately and periodically in the direction of propagation of incident light. According to the above-described novel configuration, the efficiency of converting incident light into a second harmonic is greatly increased.
In the optical device, the piezoelectric layer preferably functions as a waveguide generating a second harmonic.
In the optical device, the piezoelectric layer preferably has a flat surface.
According to the above-described configuration, since the piezoelectric layer has a flat surface, the leakage of light transmitted in the piezoelectric layer is prevented and minimized. Thus, the light loss is greatly reduced and the efficiency of converting incident light into a second harmonic is greatly increased.
In addition, in order to overcome the above-described problems, preferred embodiments of the present invention provide a method for manufacturing an optical device including the steps of forming on a substrate dielectric layers to transmit incident light substantially parallel to the surface of the piezoelectric layer, wherein the dielectric layers include first regions having an axis orientation in a first direction and second regions having an axis orientation in a second direction, and the first direction is opposite the second direction, and the first and second regions are adjacent to each other, and forming the dielectric layers which cause a piezoelectric layer to have an axis orientation in a first direction on a portion of the substrate which causes the piezoelectric layer to have an axis orientation in a second direction, and forming the piezoelectric layer on the substrate and dielectric layers.
According to the above-described configuration, the piezoelectric layer generating a second harmonic is prepared with high reproducibility and at reduced cost by forming the dielectric layers, wherein the piezoelectric layer has the first and second regions which have different orientations and are adjacent each other.
The above and other elements, features, and advantages of the present invention will become clear from the following detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings.